Bone tracking with a gyroscope sensor in computer-assisted surgery

Abstract

A system tracks an object in computer-assisted surgery. The system comprises a sensor unit secured to the femur. Gyroscopes on the sensor unit produce readings related to orientation data about three axes of rotation. A tracking unit receives the gyroscope readings. An axis calibrator on the tracking unit comprises a calculator for adding at least part of the gyroscope readings for specific movements of the object about a desired axis. An axis normalizer on the tracking unit determines an orientation of the desired axis with respect to the sensor unit from the added gyroscope readings. A tracking processor tracks the desired axis from the gyroscope readings. An interface displays orientation data for the object from a tracking of the desired axis. A method for tracking an object with a gyroscope sensor unit is also provided.

The invention claimed is: 
     
       1. A method for tracking a bone with a gyroscope sensor unit secured to the bone, comprising:
 obtaining, by a processor of a system for tracking a bone, gyroscope readings for three axes of rotation during specific movements of the bone about a desired axis, the specific movements being reciprocating movements of rotation of the bone about the desired axis with the bone and the desired axis both being fixed in position in space, the bone having an elongated shape and the desired axis being a longitudinal axis of the elongated shape; 
 summing, by the processor, at least part of the gyroscope readings; 
 determining, the processor, an orientation of the desired axis with respect to the gyroscope sensor unit by normalizing the summed gyroscope readings in the three axes; 
 tracking, by the processor, the orientation of the desired axis of the bone from the gyroscope readings; and 
 displaying, by a display of said system, tracking data from the tracked orientation of the desired axis of the bone. 
 
     
     
       2. The method according to  claim 1 , wherein summing at least part of the gyroscope readings comprises changing a direction of the gyroscope readings for all reciprocating movements in a first direction prior to summing. 
     
     
       3. The method according to  claim 1 , further comprising identifying, by the processor, any unstable gyroscope readings, and discarding the unstable gyroscope readings prior to determining the orientation of the desired axis. 
     
     
       4. The method according to  claim 3 , wherein identifying any unstable gyroscope readings comprises obtaining a motion sensor signal associated with at least some of the gyroscope readings. 
     
     
       5. The method according to  claim 1 , further comprising identifying and discarding, by the processor, outlier values from the gyroscope readings prior to determining the orientation of the desired axis. 
     
     
       6. The method according to  claim 1 , further comprising setting, by the processor, a second and a third axis to the desired axis to form a three-axis coordinate system. 
     
     
       7. The method according to  claim 6 , wherein setting a second axis comprises identifying a given axis of the sensor unit as the second axis. 
     
     
       8. The method according to  claim 1 , wherein the bone is a femur, and the desired axis is a mechanical axis of the femur. 
     
     
       9. The method according to  claim 8 , wherein the specific movements are rotations about the mechanical axis from the femur being constrained by a joint at a knee end, and by a hip joint at an opposite end. 
     
     
       10. The method according to  claim 1 , wherein the bone is a bone model or cadaver bone. 
     
     
       11. The method according to  claim 1 , further comprising displaying, by the display, information pertaining to an orientation of a tool relative to tracked orientation of the desired axis of the bone.